After a full restoration project, the last thing I expected was to see the high temp clear coat I used on my engine case halves turning amber to light brown.
I decided to resolve the problem as good as possible without pulling the engine apart. My plan was to scuff the existing case surfaces and repaint it without a clear coat. Removing all the covers and components to get down to as much case exposed as possible.

But just to be sure I did a test. I took a torque converter cover, which is aluminum and painted the cover with DupliColor DE1615 Aluminum. Then I clear coated two areas. One with DupliColor DE1636 and one with PlastKote 229. Both high temp, 500 degree clear coatings.

After 5 days, I baked the part in the oven till the temp was just under 300 degrees. The pictures tell the story. The next test needs to be clear coat on bare aluminum I guess, maybe then it would perform OK. I intend to check with the manufactures and see what they say.

I decided to just repaint with the DE1615 and no clear.... turned out real nice!

DE1636 on the left, DE1615 w/o clear coat in the middle, 229 on the right

Be sure you let each coat properly cure as it's written on the can. Then bake in two stages, the base coat is gassing off under the clear coat.

Maybe that's the secret; baking the base coat to fully cure it or give it seven days of dry time. Scuff it, then clear coat it. To the contrary the instructions on the can state to clear coat the base coat within 1 hour of applying the base coat. Oh well the engine looks good without the clear and for now that's good. If I can produce successful test results sometime then maybe I'll try again in the future. A test of just clear coat on raw aluminum will be my next test. That will yield valuable info.

I heard back from PlastiKote who makes the 229 Clear Engine Enamel. Their response was:

"Good morning Jeff,Thank you for your inquiry. The 229 Clear Coat is not a high temperature coating. This will start to discolor around 300F. I do not know of any of the aerosol companies carrying a high temperature clear. I am glad this was only a test. Please feel free to contact me if you have any further questions. Sincerely"

I guess they don't consider 500 degree Engine Enamel a high temp coating???

I contacted DupliColor through their web site and explained my dis-coloration problem with their DE1636 high temp clear coat. After answering some of their questions regarding my application process and providing upc codes and batch numbers they provided me with the response:

8/17/2011 9:34:51 AM [Agent Note]

Jeff,

Thank you for contacting Dupli-Color. We appreciate your response.

If the clear coat is turning brown it has to do with how hot the engine is getting. The easiest fix is not to use the clear coat. While the clear coat provides a little more extra protection, the Engine Enamel paint itself is durable enough to withstand the elements and resist high heat. If you would like to provide me with your full name, physical address, and how many cans you need I would be happy to send you out replacements. Please advise me if you would like me to do so.

I hope you found this information helpful. If you have any additional questions please email me back.

Sincerely,

Jill
Dupli-Color Product Support

They followed up and stated they would submit my information to the marketing department per my request and offered a refund of the paint cost, which is nice but they really need to stop selling it as a high temperature solution for clear coating engines.

I used Glisten PC on my XS650 fork legs years ago, and it's still crystal clear. It needs to be sprayed on. Also, it will dull the shine of polished aluminum slightly. It may be OK for high heat. I'll let you read up on it.

...is worth the money. I've clear coated parts that won't be affected by heat and it's very durable. It goes on kind of milky but dries really clear. The best I've used to date. I intend to spray my carbs when I finish polishing them and the oil pan and cam cover also. The engines sidecovers are accessable enough to polish but, who knows, if it holds up to the heat maybe I'll shoot them along with the forks also.

You DO lose some of the "chrome" look you get from polishing the alum, more of a OEM look, as it was coated from the factory, but holds up better with less maintance

Quote:

Originally Posted by Schming

...is worth the money. I've clear coated parts that won't be affected by heat and it's very durable. It goes on kind of milky but dries really clear. The best I've used to date. I intend to spray my carbs when I finish polishing them and the oil pan and cam cover also. The engines sidecovers are accessable enough to polish but, who knows, if it holds up to the heat maybe I'll shoot them along with the forks also.